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ATSC Digital Television

ATSC Digital Television . Advanced Television Systems Committee standards for broadcast digital television. Presented by Andrew Sonnek. Objectives of DTV. Increase picture resolution by up to 5x Support AC-3 5.1 channel audio (standard of Dolby Digital)

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ATSC Digital Television

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  1. ATSC Digital Television Advanced Television Systems Committee standards for broadcast digital television Presented by Andrew Sonnek

  2. Objectives of DTV • Increase picture resolution by up to 5x • Support AC-3 5.1 channel audio (standard of Dolby Digital) • Maximize bandwidth allocation by using complex video and audio compression • Reduce the bit rate by a factor of 50 or higher • Preserve the high level of quality required for the application

  3. DTV Picture Resolution Standards

  4. Uncompressed Video • Assuming 480p @ 30 frames/sec. * See: ftp://ftp.jacweb.jvc.com/jvcpro/justbitsfree.pdf

  5. The Challenge • The ATSC allocates 6 MHz for a single channelSo… • Over the air 6 MHz =~ 19 Mbps • Over coaxial Cable TV line =~ 38 MbpsFrom our last calculations… • Uncompressed 480p signal = 166 Mbps!!When in distress… compress!

  6. Video Compression • Film mode encoding – encoder recognizes a film source of less than 60 fps and will only encode at a rate of 30 fps or 24 fps • Uses source-adaptive processing – maximize compression techniques depending on spatial resolution, temporal resolution, and scanning rate.

  7. Video Compression • Uses the MPEG-2 compression layers as a basis for the DTV compression standard • Because of limitations of MPEG-2 standard, the DTV standard is only based on MPEG-2 standards. A DTV compressed video stream is NOT an MPEG-2 video stream so a MPEG-2 decoder will not decode DTV signals

  8. Audio Compression • Audio is compressed using the AC-3 (Digital Audio Compression Level 3) Standard developed by Dolby Labs. AC-3 is commonly known as Dolby Digital. • AC-3 supports 1 mono channel to 5.1 channels per service with multi service support up to 640 kbps total • Frequency range from 20Hz – 20kHz • Sample rate of 48kHz @ 16 bits/sample

  9. DTV Subsystems Based on International Telecommunications Union – Task Group 11/3 Diagram from ATSC Doc A/54

  10. Source Coding and Compression Subsystem • Responsible for minimizing the number of bits needed to represent the video, audio, and control data through: - Video compression - Audio compression - Encoding ancillary data

  11. Ancillary Data • Includes: - Control data - Conditional access control - Audio & video associated data such as closed captioning - Independent program services - Program guides - Text based emergency messages

  12. Service Multiplex and Transport Subsystem • Based on the MPEG standard for fixed-length transport stream packetization • Responsible for multiplexing all video, audio, and ancillary data streams, creating one data stream compatible with terrestrial and cable transmission, and inserting local programming using flags

  13. Advantages of MPEG Transport Standards • Easy to detect and correct errors while broadcasting moderately long fixed-length packets over air or cable • Can accommodate video, audio, and data • Expandable for future services • Operational with other media and standards • Packets can be easily partitioned for transfer in a link layer that supports ATM transmission

  14. PID (Packet Identifier) • Used in the packet header to identify separate audio, video, and data packets in a multiplexed stream. • Do not need to be specified in advance! • Allows for the allocation for the entire channel so data to be sent in bursts e.g. – send out an encryption key to thousands of subscribers of a pay-per-view at one time or download program related software to a “smart receiver”

  15. Transport Packet Variable length Adaptation Header 4 Byte Header Data 188 Byte Packet Header includes – synchronization bit, PID, error handling counter Adaptation Header can include – blank bits for packet sizing, keys for conditional access control, and local programming flags

  16. RF/Transmission Subsystem • Responsible for: - Channel coding - Modulation • Channel coding inserts additional data for the receiver to reconstruct the original data stream • Modulation converts the digital data stream into a transmittable signal

  17. High Data Rate Mode • Twice the bandwidth as terrestrial mode • Divides the amplitude into more data levels • Does not work as well over long distances • Terrestrial mode used for most over-the-air broadcasts

  18. Sub-channels • 6 MHz frequency can be divided up into at most 4 sub-channels • Used to broadcast multiple programming options or multimedia channels • Good for programming that does not require high resolutions

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